Dry cell and separator therefor



May 27, l952 J. J. COLEMAN DRY CELL' AND SEPRATOR THEREFOR Filed March5, 1950 Low soLuBlLl'rY."

Zgwfm/zfmf maa/124 Patented May 27, 1952 DRY CELL AND SEPARATOR THEREFORJoseph J. Coleman, Freeport, Ill., assignor to Burgess Battery Company,Freeport, Ill., a corporation of Delaware Application March 3, 1950,Serial No. 147,509

9 Claims.

This invention relates to improvements in dry cells and particularly todry cells having zinc as the negative electrode, an example of which isthe common and well known Leclanche cell. The invention also relates toan improved separator for arrangement between the zinc electrode and thedepolarizing mix of such a cell.

In cells of the type in question, the zinc of the negative electrode isconsumed by electrochemical corrosion in the operation of the cell andone of the important problems which has constantly confronted themanufacturer is to control this corrosion so that it proceeds uniformlyover the area of the zinc. Uneven corrosion results in decreased outputcapacity and usually causes 1ocal puncturing of the zinc electrode,which is accompanied by leakage of the electrolyte and an kearly end ofthe useful life of the cell.

It is the principal object of the invention to provide an improved drycell in which the corrosion of the Zinc electrode is uniform with theresult that maximum utilization is made of the Zinc and high outputcapacity and a long useful life are obtained.

It is another object of the invention to provide an improved separatorelement for use between the zinc electrode and the mix of the cell,which results in the improved Zinc corrosion characteristic asdescribed.

Briefly, the benefits of the invention are accomplished by providing aseparating element between the zinc electrode and the mix whichinitially contains a mercury salt which is soluble to only a verylimited extent in Water, which salt in the operation of the cell exertsa controlling elect upon the corrosion of the zinc whereby suchcorrosion is uniform. Mercury salts of substantial solubility in waterhave been used heretofore in the electrolyte of dry cells to reducecorrosion of the zinc on open circuit, but in accordance with thepresent invention it has been discovered that mercury salts of limitedwater-solubility, when incorporated in the separator between the mix andthezinc electrode, are very effective in reducing corrosion on opencircuit, and also produce a uniform consumption of the zinc duringoperation of the cell.

In the accompanying drawing, the single figure is a vertical sectionalview of a dry cell in which the improvement of the invention isincorporated.

The invention is described in connection with a dry cell of thecylindrical type such as is in common use for flashlight and otherservice. It is not limited te this form of cell but may be employed inany form of cell employing a zinc negative electrode and a substantiallynon-acid electrolyte, such as the widely used Leclanche cell. Itcomprises an open-top cylindrical zinc cup i which constitutes thenegative electrode. Upon the bottom of the cup I0 is arranged a layer ofnon-conductive material I2, which may be a disk of paperboard orpulpboard. Lining the (Cl. 13G-102) interior surface of the zincelectrode I0 above the layer I2 is a separating layer I4 of bibulous,nonconductive material such as porous paper or blotting paper.V Thisseparating sheet is prepared or treated in a manner so as to contain amercury salt having limited solubility in water as will be describedmore in detail hereinafter.

Within the cup and in contact with the bottom layer I2 and theseparating layer I4 is a mass of depolarizing mix I6, which may be ofany suitable composition, such as a mixture of powdered manganesedioxide and carbon. The mix is moistened with the cell electrolyte,which may be the usual substantially neutral aqueous solution of zincchloride and ammonium chloride. Embedded within the mix I6 is the usualupright carbon rod I8 which serves as the positive electrode of thecell. The mix I6 is in compressed condition and the layer I4 serves toseparate said mix from the negative electrode I0.

The upper ends of the zinc electrode I0 and carbon electrode I8 extendabovethe separating layer I4 and the mix I6, and the top end of thecarbon electrode has a conductive metal terminal cap 20 fitting thereon.A non-conductive top washer 22, which may be composed of paperboard orpulpboard, is arranged in spaced relation above the depolarizing mix I6to form anv expansion space 24, and a heat-fusible seal 26, which may becomposed of wax or pitch, rests upon the washer 22 and forms a sealclosure for the open top of the cup I0. A protective cylindrical jacket28 of cardboard or other suitable non-conductive material encloses theside wall of the Zinc electrode I0 in the manner usual with cells cfthis general type.

In accordance with the present invention, a mercury salt is incorporatedin the bibulous separator I4 which is soluble to only a limited extentin water. 'I'he mercury salts which are suitable for the purpose of theinvention are those which are soluble to an extent not exceeding about0.1 gram per grams of water at ordinary temperature (20 C.). Examples ofsuitable salts are mercurous chloride, HgCl, mercurous bromide, HgBr,mercurous iodide, HgI, mercurous sulfate, HgSO4, and mercurio phosphate,Hgs(PO4)2. Some of these salts are substantially insoluble in water andwhere this is true, it is desirable that they have a somewhat greatersolubility in the cell electrolyte. For example, mercurous chloride issoluble in water to the extent of 0.21 milligrams per 100 grams of waterbut in a saturated aqueous solution of ammonium chloride, which iscommonly present in Leclanche cells, it is soluble to the extent of morethan 1.35 milligrams per 100 grams or the ammonium chloride solution.Mercurio phosphate is substantially insoluble in water and is soluble ina saturated ammonium chloride solution to the extent of 9.5 grams per1.00 grams of such solution.

In accordance with the invention, the-mercury trade.

salt is presentinthe separator.. I4 initially, that is, at A,thetimejofthe assembly= or completion of the cell. The sheet-form separatorof paper may be formed in the customary process -ior making paper, thatis, by feltingthe sheet out of a Water suspension of Wood iibers ontheFourdrinier Wire of a paper-making. wet machine..

The mercury salt may befincorporated-yin: ,thev

sheet by mixing the same with the fibers in the water suspension andfeltingthe salt along. .with

, lmuch greater. ,A commundhaving, a.. chromate Vnot be present. 5..

or a dichromateiradical and which nasi-the property of inhibiting thecorrosion of metal should This class of compounds is known, andit hasbeen found that the presence `'of such a 4compound causes the beneficialaction the fibers in the sheet-making operation. '-In" this manner thesalt is distributed uniformly-over the area of the sheet. Other suitablemethods 4may .be employed, .asspraying thesheet With.a

.suspension of. the salt, ,or dipping the vsheet. .into ...suchasuspension. After thesheet Withthesalt y therein'hasbeenformed, it isdriedandcutto lpiecesci the desired size `for. insertion in'. thezinccup l0.

The amount .ofithemercury salt. .which isincorporatedds .notcriticaLand, generally, `the, same l considerations. apply. .as when awater-soluble mercury .salt is. used,.that is, an .amount should In theassembly ofY the cell, the .absorbent sepai rating layerltis.introducedinto thecup `In Yand the.miX.lG.-and..positive electrodeIfarethere- ...after introduced. The moist mix `is `compacted `byacompressing operation vand isbrought into pressure* contact with theseparatorsii .Electrolyteis -absorbed from the mix. into the separatorto` render. the t cell operative.

,When. amercury salt of limited Water solubilityisincorporated-in theseparator .i 4 ,in ac- ,cordance with theinvention` a markedimprovement. in. the.. uniformity of lelectrolytic .corrosion of. thezincis obtained. Corrosion .on open cir- .cuitisgreatlyreduced and4consumption on closed ,circuitis ,uniform overth'e areaoi the zinc elec-Whereas in the absence of. such salt the corrosion is uneven and thelocal areas of thc zinc are frequently punctured at an'undesirably l.early'` stage, the inclusion of the mercury" salt of limitedWater-solubility in the separator causes .of energy and. has a long.useful' life.

The action which produces the beneficial resultsjis believed. to beasfollows. When the electrolyt'eis .absorbed from the mix i 6 into' thelayer .I 41 it comesiinto contact with. the mercury salt L.in.said.layer and a substantial amount .of Athe salt'goes into 4solution inthe electrolyte. The

'electrolyte'.also comes into Contact with the zinc '.electrode. id andmercury is deposited from. the .dissolved salt upon the .zinc and.amalgamates with theN latter and exerts itsbenecial effect.

,Irlthecase ofv a salt having relatively .low solubili- .tyinl theelectrolyte, such asmercurous chloride,

the,.action still. takes place with great readiness,

.because asthe mercury is deposited onthe zinc it isremoved from thesolution and more ofthe ,mercury salt-is readily dissolved. This actioncontinues progressively .until a protective mercury,factor. is..acquiredvby the zinc. Thel eiect `is substantially. .thesamaas if thesolubiltywere described herein to be undesirably retarded.

Asfadditionalfadvantages of the invention, the

.-use-.of the imercury salt of limited Water solubility `avoids theinjurious effects which are frequently encountered by workers engaged incell manufacture Where highly Water-soluble mercury salts are used. Inaddition, the use of the salts of limited Vsolubility avoidsdeleterious.` effects upon 'cellmanufacturing equipment.. :When-.so-

lutions containing dissolved. mercury.salts come in. contact with metal,such as iron, brass,.,copper, etc, small amounts of the. mercury: fare.deposited upongthe metal and cause.-thellatterrtobe contaminated withthe mercury .withl deleterious eiects upon. the machinery.

1 What. is .claimed is: p LA .separator for...dry cells'-l comprisinga.bibulous sheet carrying. amercurysaltwhich .is

.soluble in water. to anextent notexceeding. about 0.1 gram. per 100gramsv .of .water.

In. a dry` cell, ,the combination of.. a .zinc negative electrode, apositive electrode, a. body -of mix. between. said electrodes,said'.mix..being moistened With an .aqueouselectrolyta a bibulousseparatorbetween .said mix and. said..negative electro de, said.separator. initially-carrying. a ,mercury salt which .is soluble in.Water-.taart extent not exceeding about 0.1 gramper .100z .gramsiofwater, saidv cell being substantially. free .ci a com- .pound having aradical fromthe groupconsisting 'of the chromate and dichromateradicals.

3..A dry cell as claimed in claim .2.n..W-hich the .electrolyte contains.ammoniuinchl'orida `1.,A-dry cell as claimedin. claim 2 in-.wlfiich themercury salt is .mercurous Ichloride.

5. A dry cell as claimed in claim 2 infwhich the mercury salt ismerourous. sulfate.

6.`A. dry cell as claimed in '.claim. 2 intvhich themercury salt.- ismercurous bromide.

7.,A dry cell, as vclaimed in. claim.. ZinIWhich the .mercury salt ismercurous iodide.

. thesediiculties ,to disappear and the corrosion progresses uniformly,.and premature puncturing avoided' and the' cell deliversa large outputGal 8..A dry, cellas claimed in claim 2 in which the mercury salt ismercurous phosphate.

9. In a drycell of the Leclanche type. having. a zinc negativeelectrode,Y a positive. electrode, body of depolarizing mix between saidelectrodes, a. non-conductive separator between said mix andsaidnegative electrode,l said mix and saidseparatoribeing moistened withaqueous electrolyte, and said separator initially carrying a compoundfrom the group consisting of mercurous chloride,

mercurous bromide, mercurous iodide, mercurous sulfate and mercuriophosphate.

J OSEPH` J COLE-MAN.'

REFERENCES {ITED The' following references are of record-inthe file ofthis patent:

UNITED STATES PATENTS Number Name Date 828,335 Post Aug..,14`,19061,140,826 Hoppie May. 25,` v1,915 2,301,390 Forsythe Nov.. 10, 19422,422,045 Ruben --.June 10. 1947 Sholl. The Dry Battery, 1940. edition,page.

2. IN A DRY CELL, THE COMBINATION OF A ZINC NEGATIVE ELECTRODE, APOSITIVE ELECTRODE, A BODY OF MIX BETWEEN SAID ELECTRODES, SAID MIXBEING MOISTENED WITH AN AQUEOUS ELECTROLYTE, A BIBULOUS SEPARATORBETWEEN SAID MIX AND SAID NEGATIVE ELECTRODE, SAID SEPARATOR INITALLYCARRYING A MER-